Power supply apparatus

Abstract

A power supply apparatus includes a generator, lead-battery, and second-battery. Open-circuit voltages and internal resistances of the batteries are determined so that: there is a point, where the open-circuit voltage of the second-battery coincides with that of the lead-battery, in a region on a smaller-residual-capacity side relative to a range of use in an entire-residual-capacity range of the second-battery; the open-circuit voltage of the second-battery is larger than that of the lead-battery in the range of use of the second-battery; the internal resistance of the second-battery is smaller than that of the lead-battery in a charging state of the generator; and a terminal voltage of the second-battery in a state where a maximum charge current is passed through the second-battery is smaller than a regulated voltage in a power-generation state of the generator. An opening/closing section is closed in at least one of a power-generation state and a load-activated state.

What is claimed is: 
     
       1. A power supply apparatus which includes a generator, a lead battery, and a second battery, the lead battery and the second battery being connected in parallel with the generator, and in which electric power is supplied from the lead battery and the second battery to an electrical load, the apparatus comprising:
 a protective control section which limits an amount of charge to the second battery to protect the second battery from overcharge, while limiting an amount of discharge from the second battery to protect the second battery from overdischarge, such that a residual capacity of the second battery falls within a predetermined range of use determined in an entire residual capacity range; 
 an opening/closing section which is provided to a connection path electrically connecting between the lead battery and the second battery and is turned on and off to connect and disconnect between the lead battery and the second battery; and 
 an opening/closing control section which controls the opening/closing section, wherein 
 open-circuit voltages and internal resistances of the lead battery and the second battery are determined so that
 there is provided a point, where the open-circuit voltage of the second battery coincides with the open-circuit voltage of the lead battery, in a region on a smaller residual capacity side relative to the range of use in the entire residual capacity range of the second battery, 
 the open-circuit voltage of the second battery is larger than the open-circuit voltage of the lead battery in the range of use of the second battery, 
 the internal resistance of the second battery is smaller than the internal resistance of the lead battery in a charging state created by power generation of the generator, and 
 a terminal voltage of the second battery in a state where a maximum charge current is passed through the second battery is smaller than a regulated voltage in a power-generation state of the generator, and 
 
 the opening/closing control section makes the opening/closing section an off state in at least one of the power-generation state of the generator and a load-activated state where the electrical load is activated. 
 
     
     
       2. The power supply apparatus according to  claim 1 , wherein
 an inclination representing change of the open-circuit voltage relative to the residual capacity is different between a smaller residual capacity side and a larger residual capacity side relative to an intermediate point in the range of use of the second battery, and the inclination is larger on the smaller residual capacity side than on the larger residual capacity side. 
 
     
     
       3. The power supply apparatus according to  claim 1 , wherein
 a voltage characteristics line representing change of the open-circuit voltage relative to the residual capacity in the entire residual capacity range of the second battery has inflection points at which the inclination is changed, and the inflection points are respectively set on a smaller residual capacity side and a larger residual capacity side relative to the range of use in the entire residual capacity range. 
 
     
     
       4. The power supply apparatus according to  claim 1 , wherein
 the second battery has a voltage characteristic including a first region in which an inclination representing change of the open-circuit voltage relative to the residual capacity is smaller, and a second region in which the inclination representing change of the open-circuit voltage relative to the residual capacity is larger than that in the first region, 
 the apparatus further comprises: 
 a first calculation section which calculates, in a state where the second battery resides in the first region, the residual capacity of the second battery based on a sum of the charge/discharge currents in the second batter, and 
 a second calculation section which calculates, in a state where the second battery resides in the second region, the residual capacity of the second battery based on the open-circuit voltage of the second battery by using a correlation characteristic defining a relationship between the residual capacity and the open-circuit voltage of the second battery. 
 
     
     
       5. The power supply apparatus according to  claim 4 , further comprising a region determination section which calculates an amount of change of the open-circuit voltage or a value corresponding to the amount of change in a situation in which a charge/discharge current flows through the second battery, to determine whether the second battery is in a state of residing in the first region or in a state of residing in the second region, based on the amount of change of the open-circuit voltage or the value corresponding to the amount of change or based on the residual capacity or the open-circuit voltage obtained by using a correlation characteristic defining a relationship between the residual capacity and the open-circuit voltage. 
     
     
       6. The power supply apparatus according to  claim 4 , wherein
 the voltage characteristic of the second battery includes, as regions overlapping with the range of use, a high SOC region in which the residual capacity is higher, and a low SOC region in which the residual capacity is lower than that in the high SOC region and in which the inclination representing change of the open-circuit voltage relative to the residual capacity is larger than that in the high SOC region, 
 the voltage characteristic of the second battery has steep regions in which the inclination representing change of the open-circuit voltage relative to the residual capacity is steeper than that in the range of use, on a lower SOC side relative to the low SOC region and a higher SOC side relative to the high SOC region, 
 the first calculation section calculates the residual capacity of the second battery when the residual capacity of the second battery is in the high SOC region, assuming that the second battery resides in the first region, and 
 the second calculation section calculates the residual capacity of the second battery when the residual capacity of the second battery is in the low SOC region and the steep region, assuming that the second battery resides in the second region. 
 
     
     
       7. The power supply apparatus according to  claim 6 , wherein
 the first calculation section performs a first calculation process calculating the residual capacity based on the sum of the charge/discharge currents and a second calculation process calculating the residual capacity by using the correlation characteristic, 
 when the residual capacity of the second battery is in the high SOC region, the first calculation section calculates the residual capacity of the second battery by the first calculation process, 
 when the residual capacity of the second battery is in the low SOC region, the second calculation section calculates the residual capacity of the second battery by both the first calculation process and the second calculation process, and 
 when the residual capacity of the second battery is in the steep region, the second calculation section calculates the residual capacity of the second battery by the second calculation process. 
 
     
     
       8. The power supply apparatus according to  claim 1 , wherein
 the apparatus is installed in a vehicle, 
 the vehicle has an automatic stop and restart function under which an engine is automatically stopped when a predetermined automatic stop condition is satisfied, and the engine is automatically restarted by a starting unit when a predetermined restart condition is satisfied after the engine is automatically stopped, 
 the starting unit is connected to one side of the connection path and the electrical load is connected to the other side of the connection path, with an intervention of the opening/closing section inbetween, and 
 the opening/closing control section makes the opening/closing section an on state when the engine is started by the starting unit. 
 
     
     
       9. The power supply apparatus according to  claim 8 , wherein
 the generator is connected to the engine so as to be driven and has a function of the starter, and 
 the generator is connected to on a second battery side of the connection path relative to the opening/closing section, and the electrical load is connected to a lead battery side of the connection path relative to the opening/closing section. 
 
     
     
       10. The power supply apparatus according to  claim 8 , wherein
 a maximum allowable amount of discharge, which is allowed while the engine is automatically stopped, is determined, and a residual capacity, which is obtained by adding the maximum allowable amount of discharge to a lower limit value of the range of use of the second battery, is set as an essential lower limit value in the range of use, and 
 the apparatus further comprises a discharge control section which, under a condition where the engine is in operation, controls the residual capacity of the second battery so as not to fall below the essential lower limit value in the range of use.